linux/drivers/md/bcache
Coly Li 99361bbf26 bcache: properly set task state in bch_writeback_thread()
Kernel thread routine bch_writeback_thread() has the following code block,

447         down_write(&dc->writeback_lock);
448~450     if (check conditions) {
451                 up_write(&dc->writeback_lock);
452                 set_current_state(TASK_INTERRUPTIBLE);
453
454                 if (kthread_should_stop())
455                         return 0;
456
457                 schedule();
458                 continue;
459         }

If condition check is true, its task state is set to TASK_INTERRUPTIBLE
and call schedule() to wait for others to wake up it.

There are 2 issues in current code,
1, Task state is set to TASK_INTERRUPTIBLE after the condition checks, if
   another process changes the condition and call wake_up_process(dc->
   writeback_thread), then at line 452 task state is set back to
   TASK_INTERRUPTIBLE, the writeback kernel thread will lose a chance to be
   waken up.
2, At line 454 if kthread_should_stop() is true, writeback kernel thread
   will return to kernel/kthread.c:kthread() with TASK_INTERRUPTIBLE and
   call do_exit(). It is not good to enter do_exit() with task state
   TASK_INTERRUPTIBLE, in following code path might_sleep() is called and a
   warning message is reported by __might_sleep(): "WARNING: do not call
   blocking ops when !TASK_RUNNING; state=1 set at [xxxx]".

For the first issue, task state should be set before condition checks.
Ineed because dc->writeback_lock is required when modifying all the
conditions, calling set_current_state() inside code block where dc->
writeback_lock is hold is safe. But this is quite implicit, so I still move
set_current_state() before all the condition checks.

For the second issue, frankley speaking it does not hurt when kernel thread
exits with TASK_INTERRUPTIBLE state, but this warning message scares users,
makes them feel there might be something risky with bcache and hurt their
data.  Setting task state to TASK_RUNNING before returning fixes this
problem.

In alloc.c:allocator_wait(), there is also a similar issue, and is also
fixed in this patch.

Changelog:
v3: merge two similar fixes into one patch
v2: fix the race issue in v1 patch.
v1: initial buggy fix.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Cc: Michael Lyle <mlyle@lyle.org>
Cc: Junhui Tang <tang.junhui@zte.com.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-02-07 12:50:01 -07:00
..
alloc.c bcache: properly set task state in bch_writeback_thread() 2018-02-07 12:50:01 -07:00
bcache.h bcache: fix high CPU occupancy during journal 2018-02-07 12:50:01 -07:00
bset.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bset.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
btree.c bcache: reduce cache_set devices iteration by devices_max_used 2018-01-08 13:29:00 -07:00
btree.h Merge branch 'for-4.15/block' of git://git.kernel.dk/linux-block 2017-11-14 15:32:19 -08:00
closure.c bcache: mark closure_sync() __sched 2018-01-08 13:29:00 -07:00
closure.h bcache: closures: move control bits one bit right 2018-01-09 12:18:51 -07:00
debug.c bcache: fix wrong return value in bch_debug_init() 2018-01-08 13:29:00 -07:00
debug.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
extents.c bcache: Fix building error on MIPS 2017-11-24 16:22:58 -07:00
extents.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
io.c bcache: fix misleading error message in bch_count_io_errors() 2018-01-08 13:29:00 -07:00
journal.c bcache: fix high CPU occupancy during journal 2018-02-07 12:50:01 -07:00
journal.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig bcache: Kill dead cgroup code 2014-03-18 12:22:35 -07:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
movinggc.c block: move bio_alloc_pages() to bcache 2018-01-06 09:18:00 -07:00
request.c bcache: fix unmatched generic_end_io_acct() & generic_start_io_acct() 2018-01-08 13:29:00 -07:00
request.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
stats.c md: Convert timers to use timer_setup() 2017-11-14 20:11:57 -07:00
stats.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
super.c bcache: fix misleading error message in bch_count_io_errors() 2018-01-08 13:29:00 -07:00
sysfs.c bcache: add journal statistic 2018-02-07 12:50:01 -07:00
sysfs.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trace.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
util.c block: move bio_alloc_pages() to bcache 2018-01-06 09:18:00 -07:00
util.h bcache: fix high CPU occupancy during journal 2018-02-07 12:50:01 -07:00
writeback.c bcache: properly set task state in bch_writeback_thread() 2018-02-07 12:50:01 -07:00
writeback.h bcache: fix writeback target calc on large devices 2018-01-08 13:29:00 -07:00